The invention relates to a document size detecting device, and more particularly, to a document size detecting device which is capable of automatically detecting the size of an original document set on a transparent plate.
In recent years, a number of image forming device such as an electrophotographic copying apparatus employs a constitution wherein an original document set on a transparent plate is exposed to form an image corresponding to that of the original document by moving an optical system. In an electrophotographic copying apparatuses in particular among image forming apparatuses such as above, there is provided an electrophotographic copying apparatus comprising a document size detecting function for automatic detection of the size of an original document set on a transparent plate, an automatic paper selecting function for automatic feeding from a paper cassette the paper of a size that conforms to the copying magnification set based on the detected document size, and an automatic copying magnification setting function which automatically calculates the copying magnification from the detected document size and the paper size to cause to accomplish variable power of an optical system.
Conventionally, there has been provided a document size detecting device used for the type of an electrophotographic copying apparatus such as above wherein;
(A) a sensor bar having a sensor at the tip thereof is caused to interlock with a motion to close a document presser and further caused to swivel in parallel with a transparent plate thereby to automatically detect the size of an original document in the bases on a documentdetecting time (Unexamined Japanese Utility Model Publication No. 201558/1982).
(B) a coloring member provided at a prescribed position of a document presser, a photo emitter which irradiates light on the coloring member, a photo receptor which receives the reflecting light from the coloring member, and a driving means for retracting the foregoing photo emitter to a position to allow free movement of an optical system, so that the document size is automatically detected in accordance with the signal from the photo receptor which corresponds to a portion interrupted by an original document and a portion not interrupted by the original document (Unexamined Japanese Patent Publication No. 22424/1981).
(C) a pair of optical sensors installed at a prescribed position of the moving frame which supports an optical element, one of the foregoing optical sensors detects the end of the original document and the other optical sensor of the foregoing reads the mark of an indication plate thereby detecting the document size automatically (Unexamined Japanese Patent Publication No. 48759/1982).
(D) one end of the foregoing arm is connected to the prescribed position of the body of an image forming apparatus, and other end of the arm is connected to prescribed position of the moving frame which supports the optical element, so as to cause an arm capable of folding at a prescribed part to extend and contract by interlocking the arm with the movement of the optical system and a plurality of optical sensors are installed on the top surface of the foregoing arm corresponding to an original document of various fixed forms (Japanese Patent Application No. 148780/1985, US Patent Application No. 880,859, European Patent Application No. 86109130.4).
The document size detecting device described in (A) of above has a problem wherein when the speed to close the original document presser is changed, the document size is detected accidentally because the document detecting time is changed pursuant to a change in the speed to close the original document presser.
Further, the document size detecting device of (B) of above has a construction which becomes complicated because the device requires a special driving mechanism to shunt the photo receptor. Besides, because the time to shunt the photo receptor is necessary between a point where the size detection of an original document is completed and a point where the exposure of the original document is started, there was a problem that it took a long time from a point where the key operation was accomplished to start exposure of the original document to a point where the exposure of the original document was completed.
Furthermore, the document size detecting device of (C) of above involved a problem in which because it was necessary to reciprocate once the moving frame which supports the optical element each time the size of the original document is detected, it took a long time after the key operation was accomplished to start exposure of the original document and before the exposure of the original document was completed.
For the purpose of eliminating the above problems, the applicants of the present invention developed a document size detecting device having a constitution as described in (D) of above, wherein no special driving means for shunting is necessary and it is possible to reduce the time from a point where the prescribed key operation is accomplished to a point where the exposure of the original document is completed. More particularly, this document size detecting device comprises an arm which is foldable at a prescribed portion, one end of the arm is connected to a prescribed position of the body of the electrophotographic copying apparatus, the other end thereof is connected to a prescribed position of the moving frame which supports the optical element so as to extend and contract following the movement of the moving frame, a plurality of optical sensors are installed at mutually different prescribed positions of the foregoing arms, and the output signal from the optical sensor is caused to be led as it is to the control section installed inside a device such as an electrophotographic copying apparatus thereby accomplishing the detection of the document size based on the output signals from optical sensors.
By the above arrangement, when the moving frame which supports the optical element is located at the home position, it is possible to dispose the optical sensor caused to correspond to original documents of various fixed forms by extending the arm. Therefore, by determining a specific optical sensor which has detected an original document, it becomes possible to automatically detect the size of the original document Moreover, after the document size is detected, exposure of the original document can be accomplished without any inconvenience because the arm is foldable following the movement of the moving frame.
However, in an electrophotographic copying apparatus of optical system moving type as described in (D) of above, it is necessary to provide the feeder line to supply the electric power to the light source for illuminating the original document with such number of degrees of freedom as to allow the feeder line to follow the movement of the optical system but if this feeder line is caused to hang, the feeder line touches the parts installed in the area around the feeder line causing subsequent wear or is hooked on the foregoing parts thereby hindering the movement of the optical system.
For the reasons of above, in a conventional electrophotographic copying apparatus, there used to be a problem wherein it is necessary to provide a additional mechanism to hold the feeder line freely movable (refer to Unexamined Japanese Patent Publication No. 98429/1985 for example, in which a flexible coil spring is used instead of the arm and the feeder line is passed through coil spring), thus the mechanisms of the electrophotographic copying apparatus become complicated and an additional space is required inside the electrophotographic copying apparatus.
On the other hand, because the arm is folded frequently, the durability of the feeder line at the folding section of the arm becomes a problem. For example, in Unexamined Japanese Utility Model Publication No. 2323/1987, the feeder line is installed at the end of the arm on the side where the arm is connected to the moving frame of the optical system, along the side of the inside where the connecting support shaft is folded. Therefore, the radius of the bend or curve of the feeder line becomes small while it is folding, a considerably large concentrated stress is locally applied to that part of small radius when the arm extends and contracts following the movement of the optical system, thereby making it easy for the feeder line to be broken and making it difficult to replace once the feeder line is broken.